The emergency or fire escape ladder art is replete with collapsible ladders deployable from a stacked, folded or telescopically nested storage condition interiorly or exteriorly below, between or in front of a window or other building opening. Of the many important features of a collapsible ladder, strength provides one unvarying parameter as the ladder must be capable of withstanding the weight of one or possibly several people at one time. The attempt to optimize other parameters such as cost, compactness of storage, ease of deployment and ease of descent has produced a wide variety of emergency ladders.
For example, U.S. Pat. No. 4,098,372 describes a collapsible ladder having flexible rail members and identically shaped rungs which seat upon one another and result in a very compact storage condition. Ladders of this type, although inexpensive and easy to deploy, are typically difficult to descend because the rungs hang so close to the building being exited that it is difficult for the climber to plant his feet firmly on the rungs. U.S. Pat. No. 1,053,135 discloses a fire escape ladder with a pair of flexible rail members and an outwardly extending step which is held away from the building and in a horizontal position by a pair of angled chain link sections. U.S. Pat. No. 1,753,798 shows a fire escape with a single pair of flexible rail members and horizontal rungs supported perpendicularly therebetween. U.S. Pat. No. 3,762,501 discloses a collapsible ladder assembly having a single pair of flexible rail members with vertically spaced rungs secured thereto and having disc members which are intended to space the ladder in use from the side of the building. U.S. Pat. Nos. 3,692,145 and 3,847,246 disclose escape ladders having horizontal support members which hold the rungs a distance from the building to provide stability for descent. U.S. Pat. No. 4,434,871 discloses an escape ladder having rungs with inward extensions to hold the rungs away from the wall of the building. U.S. Pat. Nos. 3,415,341 and 4,445,589 also disclose emergency fire escapes wherein each rung has inward extensions and wherein the rung is wide enough to provide a good wide tread for the climber's foot. U.S. Pat. No. 4,260,039 provides a collapsible ladder assembly having an accordion-like structure and wherein every other rung is substantially wider than the immediate rungs thereby providing adequate space for the climber's ft. U.S. Pat. Nos. 3,344,886 and 3,677,366 disclose additional fire escape devices deployable from an upper story window or similar emergency exit. Although many of the above ladders meet some of the important features such as ease of descent and ease of deployment, none satisfactorily meets all the desired features without being expensive, complicated or cumbersome.
What is needed is a collapsible ladder assembly which provides improved stability during descent while at the same time providing a small, inconspicuous storage size and which is easy to deploy in an emergency.